This application relates to German patent application 100 19 562.8 filed Apr. 20, 2000; and to which Priority is claimed.
The invention relates to an optical element housing or mounting connector, in particular for lens elements in semiconductor-lithography projection printing machines.
Mountings of lens elements for the forming of a lens system are generally connected to one another by a large number of screws arranged in a distributed manner around the circumference. However, the tightening forces of the screw connections produce certain deformations of the mounting and consequently of the lens elements or the optical system. In particular, depending on the number of screws, this produces a waviness, which has adverse effects on the optical element, for example a lens element. Although the deformation of the optical system generally takes place only in the nanometer range, under some circumstances this deformation is problematical, for example in semiconductor-lithography projection printing machines.
The present invention is based on the object of providing a connecting technique for mountings and housings of optical elements which does not produce any adverse effects on the optical system.
Electro-permanent magnets have previously been used in production engineering as clamping elements in order to fix workpieces for a machining operation and subsequently release them again after the workpiece has been machined. Electro-permanent magnets combine the essential design features of electro systems with those of cure permanent systems. In addition to permanent magnets, an excitation coil is provided. After switching on the excitation coil, the initially magnetically neutral permanent magnets are magnetized by the magnetic field of the coil. Once this activating operation has taken place, the current supply can be disconnected. The magnetic field and consequently the magnetic forces are subsequently generated exclusively by the action of the permanent magnets. Therefore, no further power needs to be supplied during the entire clamping and machining operation for machining the workpiece. The cable connection between the magnet and the control part is disconnected after activation of the magnet.
It has now been recognized in an inventive way that the principle of electro-permanent magnets as actual clamping devices can also be used for the permanent connection of mountings and housings or optical elements if they are integrated in a suitable way into mountings or housings or are connected to the mountings or housings.
One of the main advantages of the connector according to the invention is that mountings and housings can be adjusted exactly in relation to one another during assembly, with only very small or absolutely no adhering forces being present during the adjusting operation. This means that individual parts of the lens system can be displaced exactly, in order for example to be able to set the optical axis accurately. Only after completion of the adjusting operation is the electro-permanent magnet magnetized by the coil and receives its adhering force in this way for the exact connection of the individual mountings or housings to one another. The selected adhering force is sustained for a long time.
A further advantage of the connector according to the invention is that the clamping force can be controlled and set very accurately by appropriate activation of the coil.
According to the invention, the electro-permanent magnets make it possible to dispense with screw connections, at the same time not only avoiding deformations of the optical system but also significantly shortening the assembly time. In addition, mountings or housings no longer have to be drilled or threads cut during prefabrication, also making it possible to dispense with interrupted cuts. Furthermore, turned reliefs of outer mountings for screws are no longer required. Instances of circumferentially distributed waviness of the optical element are completely avoided, since there are no longer any irregular clamping effects caused by the screw connection.
A further advantage of the connector according to the invention is that, for example, lens-element mountings or any kind of drill-hole limitations can be turned through any angle and displaced in any way desired. This is of advantage particularly for lens system adjustment in systematic adjustment processes.
In an advantageous design of the invention, it may be provided that, for example, mountings or housings are provided with recesses in which an electro-permanent magnet is arranged in each case, or that an adjusting ring with an annular electro-permanent magnet is arranged in each case between two mountings or housings.
Depending on the arrangement of the electro-permanent magnets and possibly intermediate rings, the mountings can be magnetic or non-magnetic.
A very advantageous development, with a new application at the same time, is obtained if the optical element is designed as a manipulator in the z direction by a form of configuration of planar surfaces on which the magnetic force acts.
This configuration provides the possibility of changing or influencing a lens system with respect to its optical imaging. With the aid of a specific configuration of planar surfaces, for example in the form of open wedge surfaces or stepped ring surfaces, which are provided with subregions projecting freely on the inner circumference, the associated optical element, for example a lens element, can be deformed in a specifically selective way. On account of the projecting subregions, bending is applied by the induced magnetic force and this bending consequently also acts in the same way on the optical element, hereby a specifically selective deformation can be achieved as a z manipulator.